[ios-sdk] Unit tests should link to new frameworks optionally.
[ios-sdk] Unit tests should link to new frameworks optionally.

Summary:
Unit test project was set to require Accounts and AdSupport frameworks. Making them optional so unit tests run on pre-iOS 6.0
simulators.

Test Plan:
- Ran unit tests on iOS 4.3 simulator.

Revert Plan:

Reviewers: jacl

Reviewed By: jacl

CC: msdkexp@

Differential Revision: https://phabricator.fb.com/D579012

Subsplash/facebook-ios-sdk,ArtLapitski/facebook-ios-sdk,1234-/facebook-ios-sdk,shepting/facebook-ios-sdk,tipbit/facebook-ios-sdk,wooga/facebook-ios-sdk,hibu/facebook-ios-sdk,1234-/facebook-ios-sdk,ShareKit/facebook-ios-sdk,ShareKit/facebook-ios-sdk,1234-/facebook-ios-sdk,flovilmart/facebook-ios-sdk,Subsplash/facebook-ios-sdk,flovilmart/facebook-ios-sdk,shepting/facebook-ios-sdk,taptaptap/facebook-ios-sdk,shepting/facebook-ios-sdk,taptaptap/facebook-ios-sdk,hibu/facebook-ios-sdk,Subsplash/facebook-ios-sdk,hibu/facebook-ios-sdk,Amnysia/facebook-ios-sdk,flovilmart/facebook-ios-sdk,shepting/facebook-ios-sdk,taptaptap/facebook-ios-sdk,ArtLapitski/facebook-ios-sdk,ShareKit/facebook-ios-sdk,TimeIncOSS/facebook-ios-sdk,tipbit/facebook-ios-sdk,shepting/facebook-ios-sdk,1234-/facebook-ios-sdk,Amnysia/facebook-ios-sdk,beamly/facebook-ios-sdk,hibu/facebook-ios-sdk,Amnysia/facebook-ios-sdk,ArtLapitski/facebook-ios-sdk,beamly/facebook-ios-sdk,hibu/facebook-ios-sdk,1234-/facebook-ios-sdk,ArtLapitski/facebook-ios-sdk,TimeIncOSS/facebook-ios-sdk,anthonylai/facebook-ios-sdk,FiftyThree/facebook-ios-sdk,flovilmart/facebook-ios-sdk,flovilmart/facebook-ios-sdk,tipbit/facebook-ios-sdk,TimeIncOSS/facebook-ios-sdk,wooga/facebook-ios-sdk,anthonylai/facebook-ios-sdk,beamly/facebook-ios-sdk,anthonylai/facebook-ios-sdk,FiftyThree/facebook-ios-sdk,wooga/facebook-ios-sdk,FiftyThree/facebook-ios-sdk